<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>电子表</title>
    <script>
        function startTime() {
            var today = new Date();
            var h = today.getHours();
            var m = today.getMinutes();
            var s = today.getSeconds();
            m = checkTime(m);
            s = checkTime(s);
            document.getElementById('txt').innerHTML = h + ":" + m + ":" + s;
            t = setTimeout(function () {
                startTime()
            }, 500);
        }

        function checkTime(i) {
            if (i < 10) {
                i = "0" + i;
            }
            return i;
        }
    </script>
</head>
<body onload="startTime()">
<div id="txt"></div>
</body>
</html>